The present invention relates generally to photolithographically patterned spring contacts, and more particularly to structures incorporating electrical microsprings with thermal structures to provide both microspring-based electrical contacts as well as target device cooling.
The maximum complexity of an integrated circuit is limited by yield issues. In some applications, highly complex functions can be implemented at lower cost by using multiple integrated circuits mounted to a base substrate using bonding of multi-chip modules or flip-chip packages. Ball grid array (BGA) or flip chip (FC) bonding utilizes a two-dimensional grid of solder balls for die attachment which are heated to form a metallurgical junction. Details of BGA and FC bonding are well known.
In general, solder balls need to be large in order to have the necessary mechanical compliance against shear stresses induced by differences in the coefficient of thermal expansion (CTE) between the die and the base substrate, which results in a long thermal path and limited thermal conductivity. In addition, solder-bonding restricts the choice of base substrate to avoid the mechanical stress induced by a difference in CTE between the die and base substrates. The solder reflow process requires high temperature usually (>200 C). In certain applications, an integrated circuit is attached using solder with a polymer underfill between the integrated circuit and the base substrate in order to minimize the mechanical stress on the solder balls. The required underfill material has poor thermal conductivity, and as a result the heat transfer from the integrated circuit to the base substrate may be poor. A mechanical heat sink may be mounted to the back of the integrated circuit die, but in many applications such as cell phones, laptop and tablet computers, and other compact devices there is insufficient height to permit an adequately tall heat sink to be used. Further still, heat sinks add cost, weight, and manufacturing complexity.
Microsprings are an alternative to solder bonding for electrical interconnect between components such as between a semiconductor die and base substrate. Microsprings have been used for electrical contact to a semiconductor die, for example in probe cards for semiconductor die testing. However, in order to use microsprings as electrical contacts for semiconductor die in-field applications, certain semiconductor test arrangements, and so on, it is necessary to provide a thermal path that is at least as good as that provided by solder bonding, and preferably improve the thermal path compared to solder bonding. A solution to the thermal problems associated with the use of microsprings in applications such as multichip modules has not been disclosed.